In a conventional Global System for Mobile Communication (GSM) network system, the Base Station Controller (BSC) side is required to convert the wireless side voice from compressed codes (such as HR/FR/EFR codes) to non-compressed G.711 codes. The Media Gateway (MGW) on the core network side is required to convert the non-compressed G.711 codes to Adaptive Multi-Rate (AMR) compressed codes. Furthermore, the MGW is required to convert the bearer mode between TDM bearer on one side and IP bearer on the other side. In order to realize these conversions, a Transcoder and Rate Adaption Unit (TRAU) or a TransCoder (TC) is typically inserted in the BSC of the GSM network system, and a TC is inserted in the MGW, for corresponding conversions of voice codes and bearer modes. Such conversions may lower voice quality, waste a lot of costly TC resources, and increase equipment costs. At the same time, since G.711 coding is used in the A interface, each path of the calls occupies a bandwidth of 64 k, causing a waste of long-distance transmission resources from the BSC to the MGW.
To save the TDM transmission resource between the BSC and the MGW, an improved method presently proposed is to move the TRAU from the BSC side to the MGW side to collocate the TRAU with the MGW, and an Ater interface is provided between the BSC and the TRAU for transmitting voice and data in format of TRAU frames. Since each call of the Ater interface occupies a bandwidth of only 16 k, four calls may be multiplexed into one TDM slot, saving the valuable long-distance transmission resource between the BSC and the MGW.
Although the improved method mentioned above solves the problem of wasting the long-distance transmission resource between the BSC and the MGW, TCs are still required to be inserted in both the TRAU and the MGW for the conversion of bearer modes, which also suffers voice quality deterioration and TC resource wasting due to multiple code conversions.